Almost all dental restorations are placed on dentin which is covered by a layer of microcrystalline debris--the so-called "smear layer". A recent IADR symposium on the smear layer pointed out how little is known about the influence that this layer has on dentin permeability and the reactivity of both the smear layer itself and the underlying sound dentin to reagents designed to react with the calcium and collagen components of dentin. Little is known regarding the particle size distribution or porosity of smear layers produced with low vs high speed burs, sand paper discs vs diamond wheels. No systematic efforts have been directed to quantitate smear layer thickness or the effects of smear layers created by the above methods on dentin permeability. Numerous manufacturers have developed "dentin bonding agents" to facilitate the "bonding" of restorative resins with dentin covered by a smear layer. Such agents should greatly reduce dentin permeability but no such quantitative studies have been done. The proposed research will evaluate the effects of smear layers on dentin permeability measured as hydraulic conductance (Lp). Lp determinations will also be done to determine the effectiveness of various physical and chemical methods of removing smear layers. The reactivity of the remaining dentin surfaces will be evaluated by measuring the uptake of 45Ca and 3H-amino group reagents. Smear layer thickness will be calculated from the Ca, P and hydroxyproline contents of smear debris sonicated off of dentin. In vivo measurements of the decrease in dog dentin permeability following cavity preparations will continue in an effort to discover the underlying mechanism(s). As the phenomenon may be due to an axon reflex, the afferent limb will be eliminated by surgically denervating the mandibular nerve and/or superior cervical sympathetic nerve 3-4 weeks prior to cavity preparation. The efferent side of the reflex will be blocked by placing substance P antagonists in the cavity or by iv administration of anti-inflammatory agents like dexamethasone, aspirin, etc. New approaches at reducing dentin permeability, acutely, will be tried such as topical application of fibrinogen solution followed by topical application of thrombin.